Capacitive components can be used in a versatile manner, for example, in the field of power semiconductors. Semiconductors, such as an IGBT (insulated-gate bipolar transistor) or a MOSFET (metal-oxide-semiconductor field-effect transistor), need to be wired to external capacitive components in order to meet high current and voltage requirements. In order to obtain a high efficiency of these switches, it is necessary for the external capacitive components to be connected to the semiconductor switches with the lowest possible inductance; in other words, it is necessary for the external capacitive components to have a small self-inductance and to be connectable close to the semiconductors. In addition, high temperatures occur, which on the one hand are desirable, since high temperatures at the active semiconductor zones of the component increase efficiency, but on the other hand complicate the connection technique. A key requirement of the component is thus a high capacitance density and good insulation capability at high temperatures. Film capacitors and aluminum electrolyte capacitors are eliminated under these conditions due to the technology-induced temperature limitation thereof. However, known capacitors based on barium titanate also have not been able to meet these requirements beforehand. The reason lies firstly in the requirement of external contacting resistant to high-temperature change and secondly in the unfavorable material properties of the increasingly poorer insulation at higher temperatures.
The external contacting of a ceramic capacitor component should perform a number of tasks: firstly, the connection should have sufficient mechanical stability to connect the component fixedly to the rest of the electronic circuit arrangement (for example, to a DCB substrate (direct copper bonded board substrate)). At the same time, such a connection is exposed to mechanical stresses, which may be induced by electrostrictive forces during operation and temperature changes. Temperature change can be induced by the surrounding environment or can be produced by natural heating of the component as current flows through during the semiconductor switching processes. A further temperature increase can be produced within the scope of production by soldering or sintering processes, which indeed occurs only once, but, in terms of the temperature reached, is greater than the maximum permissible working temperature.
Metals with good electrical conductivity, for example, copper or silver, are well suited for ensuring the electrical requirements and the temperature stability, however the different coefficients of expansion of ceramic and metal mean that mechanical stresses at the transition of ceramic component body and external contacting negatively influence the service life of such connections. Previous design compromises use, for example, metals with lower coefficients of expansion, however these are accompanied by poorer electrical conductivity. A further possibility provides stress relief by using suitable geometries (for example, in meander form), which go against the optimization of the inductance however and also require a certain outlay in terms of the production. Furthermore, the problem of the temperature resistance of the connection during operation remains. This can be avoided in the case of a soldered connection with high-temperature solder containing lead, which is increasingly a topic of controversy due to the material (RoHs) and reliability.